The present invention generally relates to the field of magnetic sensors for sensing the position of a structure over a predetermined sensing range, and more specifically relates to a non-contacting magnetic position sensor having a stepped magnet interface that provides a magnetic field having improved linear characteristics over an extended sensing range.
Magnetic position sensors are devices that generate an electronic signal output that is indicative of the relative position of a mechanical component, such as, for example, a control shaft or rotor in the case of a rotational position sensor or a carrier mechanism or linkage in the case of a linear position sensor. Certain types of magnetic position sensors generate an electronic signal output representative of the relative position of the mechanical component without actual physical contact with the mechanical component. These types of non-contacting magnetic position sensors include a magnetic circuit that is operably coupled to the mechanical component and which is configured to produce a magnetic field having a magnetic field strength that varies along an air gap. A magnetic sensing element is positioned within the air gap and is operable to sense variations in the magnitude of the magnetic field strength in response to relative displacement between the magnetic field and the sensing element. The magnitude of the magnetic field strength is translated through the sensing element and is converted to a voltage or current output signal that is uniquely representative of the relative position of the mechanical component.
Referring to FIG. 1, shown therein is one example of a prior art magnetic position sensor 10. The magnetic position sensor 10 includes a pair of permanent magnets 12a, 12b and a pair of magnetically permeable plates 14a, 14b extending between the magnets 12a, 12b and spaced apart to define an air gap 16 therebetween. The magnets 12a, 12b and the plates 14a, 14b cooperate to form a closed magnetic circuit that produces a magnetic field having a magnetic field strength that varies along the length of the air gap 16. A magnetic sensing element 18 is positioned within the air gap 16 and is operable to sense variations in magnetic field strength as the sensing element 18 is relatively displaced along the air gap 16. Notably, the magnetically permeable plates 14a, 14b are rectangular-shaped, each defining a flat, uninterrupted inner surface 20 that is operably attached to a corresponding flat magnetic pole surface 22 defined by each of the magnets 12a, 12b. As a result, the width w of the air gap 16 is equal to the distance d between the pole surfaces 22 of the magnets 12a, 12b. 
The sensing element 18 is physically capable of being displaced along virtually the entire length of the air gap 16. When positioned at the approximate midpoint 24 of the air gap 16, the magnitude of the magnetic flux density passing through the sensing element 18 is at or near zero. As the sensing element 18 is relatively displaced on either side of the midpoint 24, the absolute value of the magnetic flux density increases in a manner proportional to the distance from the midpoint 24. However, since the magnetic field flows in opposite directions on either side of the midpoint 24, the actual value of the magnetic flux density on one side of the midpoint 24 is interpreted as being positive while the actual value of the magnetic flux density on the other side of the midpoint 24 is interpreted as being negative.
As shown in FIG. 2, the magnitude of the magnetic flux density varies in a substantially linear manner along the mid-portion 28 of the air gap 16 on either side of the midpoint 24 . However, as the relative position of the sensing element 18 approaches the end portion 30a of the air gap 16 adjacent the magnet 12a and the end portion 30b of the air gap 16 adjacent the magnet 12b, the change in magnitude of the magnetic flux density significantly deviates from that experienced along the mid-portion 28 of the air gap 16. This phenomenon at least partially results from the tendency of the magnetic flux to leak from the interfaces between the inner plate surface 20 and the magnetic pole surface 22, thereby resulting in an increased concentration of the magnetic flux density field strength in the areas adjacent the magnets 12a, 12b. This non-linearity in the magnitude of the magnetic flux density field strength adjacent the magnets 12a, 12b reduces the overall sensing range of the magnetic position sensor 10. Although an auxiliary electronic circuit may be used to compensate for these non-linear characteristics, post processing of the sensor output signal typically results in increased sensor costs and a possible decrease in sensor accuracy and reliability.
Thus, there is a general need in the industry to provide a magnetic position sensor having improved linear characteristics over an extended sensing range. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.
The present invention is directed to a magnetic position sensor having a stepped magnet interface that provides a magnetic field having improved linear characteristics over an extended sensing range. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the preferred embodiments disclosed herein are described briefly as follows. However, it should be understood that other embodiments are also contemplated as falling within the scope of the present invention.
In one form of the present invention, a magnetic position sensor is provided which includes a magnet, a pair of pole piece segments spaced apart to define an air gap, and a magnetic flux sensor. The pole piece segments form a stepped interface with the magnet to provide a magnetic field within the air gap having a varying magnetic flux density. The magnetic flux sensor is positioned within the magnetic field and is operable to sense a magnitude of the varying magnetic flux density along the air gap and to provide an output signal representative of a position of the magnetic flux sensor relative to the magnetic field.
In another form of the present invention, a magnetic position sensor is provided which includes first and second magnets, first and second pole pieces extending between the magnets and spaced apart to define an air gap, and a magnetic flux sensor. The first and second pole pieces form a stepped interface with the magnets to form a closed magnetic circuit that provides a magnetic field within the air gap having a varying magnetic flux density. The magnetic flux sensor is positioned within the magnetic field and is operable to sense a magnitude of the varying magnetic flux density along the air gap and to provide an output signal representative of a position of the magnetic flux sensor relative to the magnetic field.
In yet another form of the present invention, a magnetic position sensor is provided which includes a magnet, a pair of pole piece segments spaced apart to define an air gap, and a magnetic flux sensor. The magnet has a first pole surface, a second pole surface, and side surfaces extending between the first and second pole surfaces. The pole piece segments each include a first portion positioned adjacent a respective one of the first and second pole surfaces of the magnet, and a second portion positioned adjacent one of the side surfaces of the magnet. The magnet and the pole piece segments cooperate to provide a magnetic field within the air gap having a varying magnetic flux density. The magnetic flux sensor is positioned within the magnetic field and is operable to sense a magnitude of the varying magnetic flux density along the air gap and to provide an output signal representative of a position of the magnetic flux sensor relative to the magnetic field.
In still another form of the present invention, a magnetic position sensor is provided which includes means for generating a magnetic field, means for providing the magnetic field with a varying magnetic flux density along an axis with the means for providing forming a stepped interface with the means for generating, and means for sensing a magnitude of the varying magnetic flux density along the axis and for generating an output signal representative of a position of the means for sensing relative to the magnetic field.
It is one object of the present invention to provide an improved magnetic position sensor having a stepped magnet interface that provides a magnetic field having improved linear characteristics over an extended sensing range.